The bars around the plaza are the social infrastructure of the town — unpretentious spots where Medalla beer is served ice-cold and rum arrives with coconut water or in a simple mixed drink. The clientele is local and the atmosphere is relaxed. No one is performing hospitality; they're just drinking and talking.
In Puerto Rico's interior towns, these kinds of places are the real community spaces, especially on weekend evenings when the plaza empties and the bars fill up a little. If you speak some Spanish, or even if you don't and are willing to try, you'll likely find people happy enough to have a stranger at the bar.